1. Field of the Invention
The present invention generally relates to a brush bristle material mainly made of polytrimethylene terephthalate (PTT) and offering excellent properties to trap and release cosmetics and medicaments, and a cosmetic brush or toothbrush using the same.
More specifically, the present invention relates to a brush bristle material comprising a monofilament made of PTT and having a tapered surface at the tip of the brush hair where irregularities of 1 to 20 μm are formed at intervals of 5 to 50 μm, and a cosmetic brush or toothbrush using the same.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Synthetic fiber brushes with a tapered end are already known (Patent Literature 1 indicated below), and a number of improvement technologies have been presented to date. Examples include: a multi-step alkali processing performed after a bundle of polyethylene terephthalate (PET) fibers is dipped in a 20 weight-percent sodium hydroxide solution by around 10 mm, neutralized and then washed in order to create a sharp tip (Patent Literature 2); a tapered hair material made by spinning PTT and PET or PBT (polybutylene terephthalate) together, and then dipping the obtained monofilament hair material in a sodium hydroxide solution to have one end tapered and provide moisture absorption property, elasticity and flexibility (Patent Literature 3); and a brush bristle material made of a PET monofilament having a multi-lobed irregular cross-section, wherein one end of the hair is sharpened using a sodium hydroxide solution (Patent Literature 4). However, none of these technologies offered satisfactory properties in terms of trapping and releasing of cosmetics. Also, the hydrolysis time required for PTT is three times the time required for PBT, or even longer. Because of this difficulty to hydrolyze, PTT requires a higher cost to form into a tapered shape, even when sodium hydroxide solution is used, and has therefore been considered uneconomical.
As mentioned above, brush bristle materials comprising PET or PBT monofilaments with one longitudinal end tapered via alkali processing offer flexible tips and are replacing animal hairs as brush materials.
However, because these monofilaments have their surface smoothened by alkali processing, they offer lower powder-cosmetic trapping property compared with animal hairs having scaled surface.
Meanwhile, natural animal hairs are becoming more and more difficult to obtain as the world is growing more conscious of environmental protection issues. Accordingly, use of hair materials made of synthetic fibers is expected to grow further. However, it is difficult for these synthetic fibers to become primary materials for cosmetic brushes unless the aforementioned problems are resolved.
Addition of crimps to brush bristle materials is a known technology. An example of such technology is found in Patent Literature 5 (Japanese Patent Laid-open No. 2003-225123). This technology proposes crimps having a thickness of 5 to 30 times the thickness of the fiber and a height of 1.2 times or less the thickness of the fiber. If crimps become larger, the shape recoverability of the brush bristle material after application and removal of external forces drops, thereby affecting the brush function.
[Patent Literature 1] Japanese Patent Laid-open No. Sho 49-047618
[Patent Literature 2] Japanese Patent Laid-open No. Sho 51-116298
[Patent Literature 3] Japanese Patent Laid-open No. 2004-141504
[Patent Literature 4] Japanese Patent Laid-open No. 2002-058538
[Patent Literature 5] Japanese Patent Laid-open No. 2003-225123